1. The Field of the Invention
When different kinds of area specific positioning techniques develop, more and more useful applications are found.
2. State of the Art
RFID-antennas (Radio Frequency IDentification), which limit a controlled area by RF (Radio Frequency) radiation pattern to a certain area, in which limited RF area arriving mobile devices i.e. TAGs can be identified, have been sold. The mobile device is by nature a RFID tag, which does not need a current consuming active front amplifier in a RF receiver of the TAG as it operates in RF near field based on passive signal detection not becoming active before it arrives in an area of signal of sufficient strength, where it preferably and immediately can measure directly the coming signal without a load of the front amplifier, which load could be for example about 10 mA.
In this technology, such as for access control applications, the problem has been the fact that precisely in the location of the interior roof of the controlled building where the antenna would most advantageously be placed, the lamp is very often placed. In other words, the location of the lamp is very often the best antenna location or even the only good location. In addition, the problem is that the exterior sides of lamps are often metal, and thus they can easily distort the radiation pattern of the RFID antenna installed beside them. Thus, the antenna should be able, if necessary to replace the lamp when the antenna is to be positioned in the place reserved for the lamp.
Another major problem, especially in traditional RFID positioning, has been the fact that if positioning with exact limits in a small space is required, taking into account movement direction, two antennas have to be installed, which often require their own readers, and whose radiation patterns interfere with each other without special arrangements. Especially when broadcasting at the same time, the radiation patterns suffer from bad interference. In narrow places the antennas often must be placed near metal structures, such as door constructions, or pipes, which also cause distortions to radiation patterns, and for example at about 50 cm distance, can even destroy the radiation pattern.
Even if the antennas are fitted into a small space, signals are received from both antennas of the interface. In this case, without any special arrangements, area changes all the time when new signals are received even when being in place, unless the signals are measured and a TAG position is evaluated on the basis of calculations and judgements at each time point as disclosed in the patent application publication FI20095222.
A problem in automatically sending a location-based emergency call on the basis of an abnormal health status of a person in the case of a downfall is that an accelerometer should in principle be measuring acceleration all the time including before an impact possibly indicating the downfall occurs, the downfall being indicated by the end of the acceleration when the measurement of the acceleration is already too late. On the other hand, all downfalls due to worsened health status are not sudden, but a person can also be slowly and cautiously falling to the floor, when the head begins to spin. However, only the horizontal position cannot be used as an indicator of a downfall, because the horizontal position also occurs in normal situations, at least in bed.